1. Field of the Invention
The present invention relates to organic electroluminescent devices (OLEDs), and more particularly to a plastic substrate for OLED, fabrication method thereof, and device using the substrate.
2. Description of the Related Art
OLEDs are known to be highly efficient and capable of producing a broad band width of colors, Due to thin profile and wide viewing angle, OLED applications are variable and can be used as flat-panel displays. In order to achieve flatness, transparency, and high fabrication temperature tolerance, glass is a common choice for substrates. Current trends move toward light weight, slim profile, and even display on non-flat surfaces. Therefore, soft and flexible displays are currently being developed to replace glass substrates.
In order to achieve the above objects, flexible plastic (polymer) substrates have been developed for OLED, such as polycarbonate (PC), polyethylene terephthalate (PET) and polyimide but these polymer substrates have some disadvantages.
Polymer temperature tolerance is too low for fabrication, with maximum PC temperature about 129° C. and PE about 120° C. As well, polymers exhibit poor resistance to ambient humidity and oxygen penetration. Finally, PC and PET plastic substrates have difficulty achieving optical flatness and cannot be polished by chemical mechanical polishing. Thus, in conventional technology, soft and flexible plastic substrate cannot replace glass. To address the problem of OLED luminescent materials being easily damaged by ambient humidity and air penetration, addition of an encapsulation layer is conventionally employed. As disclosed in U.S. Pat. No. 5,855,994, an encapsulation layer is formed by coating flowable silicon oxide on the anode, then using UV light to solidify the encapsulation layer or a roller to press the silicon oxide film onto the anode. However, the additional encapsulantion layer is both costly and time-consuming. Additionally, the disclosed encapsulant process fails to address the stated problems of temperature intolerance and insufficient planarity.